Power generation systems generally combust hydrocarbon based fuels in order to generate energy. Such systems generally produce an end product that comprises primarily carbon dioxide and water (e.g., steam) as by-products of the energy generation process. In most cases, the stream will include varying amounts of nitrogen, oxygen, sulfur dioxide and other compounds.
Environmental pollution stemming from fossil-fueled power plants is of worldwide concern. Power plants emit air pollutants that may be toxic, e.g., toxic metals and polyaromatic hydrocarbons; precursors to acid rain, e.g., sulfur oxides (SOx) such as sulfur dioxide (SO2), and nitrogen oxides (NOx); precursors to ozone such as NO2 and reactive organic gases; particulate matter; and greenhouse gases, notably CO2. Power plants also discharge potentially harmful effluents into surface and ground water, and generate considerable amounts of solid wastes, some of which may be hazardous.
Although technologies are being developed that reduce emissions and effluents, they are often expensive and require considerable energy. Technologies have been developed and are installed on most new power plants that significantly reduce emissions of NOx, SO2 and particulates. However, CO2 remains the one emission that is currently not controlled.
Several technologies can be employed to remove CO2 from flue gases. These technologies include post combustion chemical scrubbing (such as amine scrubbing), oxygen fired combustion and chilled ammonia processes. Chemical scrubbing and oxygen fired combustion add capital cost to the plant and increase the cost of plant operation. The result is a significant increase in the cost of generated electricity.
Chilled ammonia processing (CAP) based systems provide a relatively low cost means for capturing and removing carbon dioxide from a gas stream, such as, for example, a post combustion flue gas stream.
U.S. Pat. No. 7,846,240 to Gal is directed to a chilled ammonia processing system and a method for capturing and removing carbon dioxide from a flue gas stream. Gal teaches a system that contains two absorbers, a wash vessel and a regenerator. The process however operates at low temperatures below 20° C., which causes the reaction between ammonia solutions and water to be slower. The slower reaction rate causes the use of larger vessels with attendant increased costs. The lower temperature also causes lower circulation rates, which leads to slower processes. It is therefore desirable to develop a chilled ammonia process that can operate at temperatures that facilitate a more rapid process with lower process costs and equipment of a reduced size as compared with that disclosed by Gal.